1 5/10/06 10:18 AM Page 1. Images courtesy of Beta Machinery ANALYSIS . Dynamic FOUNDATION analyses are prepared to provide recommendations for pile locations and FOUNDATION stiffness. Through the completion of these analyses the likelihood of resonance by the equipment is reduced, which results in reduced vibration within the package. FOUNDATION ANALYSIS AND DESIGN . FOR RECIPROCATING AND ROTATING EQUIPMENT. The Lack of Proper foundations Can Create Disastrous Results By Neil Purslow Editors Note This article has been ment users in the DESIGN of founda- damage it causes may be obvious and created to provide one perspective on tions where dynamic loads will be easy to detect, such as the loosening of the need for adequate ANALYSIS and de- used. As a result, many equipment oil lines and other attached equipment. sign for proper foundations for recipro- purchasers lack a consistent approach But it can also be insidious, including pleting the article, COMPRESSORTech Two cating and rotating equipment.
2 In com- to FOUNDATION DESIGN , thereby decreas- fatigue of equipment components and ing the reliability of their facilities. In piping that may go unnoticed until fail- interviewed three Calgary-based com- some cases, the lack of proper foun- ures occur. In both instances, excess panies involved in FOUNDATION DESIGN , dations can create disastrous results. vibration leads to higher operating construction and inspection services. Why worry about vibration? Vib- costs, and failures in pressure contain- Beta Machinery ANALYSIS (Brian ration is one of the leading causes of ment systems can result in gas leaks Howes, chief engineer), Primus high-frequency maintenance and fail- and serious safety concerns. Engineering (K. Pak, president) and ure of compression equipment. The Several important elements are in- Accurata Inc. (Frank Zahner, com- pression consultant) were interviewed, A variety of dynamic forces with each providing insights and ex- from a reciprocating com- periences in compressor foundations .
3 Pressor package will affect Although the companies and individ- the ANALYSIS and DESIGN of uals perform many more services than the package's FOUNDATION . It is mentioned in this article, their com- the action of the pistons that ments have been limited to certain ar- causes the biggest vibration eas for brevity. concern when designing foundations because the pis- There are a number of factors that tons create unbalanced cause gas compression equipment to forces and couples in the vibrate, and eventually break down compressor. and poor FOUNDATION DESIGN is one of them. Recent discussions with indus- try consultants revealed that many challenges in designing and imple- menting effective foundations exist. One challenge includes the lack of in- dustry specifications to guide equip- Image courtesy of Beta Machinery ANALYSIS . APRIL-MAY 2006 COMPRESSORTechTwo 5/10/06 10:18 AM Page 2.
4 Gravel pads are gen- essary to transmit vibration into the erally cheap to install. ground, said Pak. It becomes a However, they often painstaking process to ensure proper don't provide good, contact between the two surfaces. solid contact between There is no easy way to fix a gap, since the skid package and shims and grouting are not suitable op- the gravel pad for tions. The only way to fix a gap is to Image courtesy of Primus Consulting. transmitting vibration remove the package and fix the pad.. into the ground. Gaps Using pile foundations is another op- between the two sur- tion. Piles are effective at suppressing faces, as shown in this vertical movement, but are weak at picture, can only be dampening horizontal movement, said fixed by removing the Pak. Many compressor packages in skid and fixing the Western Canada are installed on metal gravel pad.
5 Piles, which generally consist of 8, 10. or 12 in. (203, 254 and 305 mm) pipe or I-beam, added Howes. Steel pipe is the most common because it is fast to install and can be used immediately, whereas concrete piles require time to cluded in a FOUNDATION ANALYSIS and de- crankshaft and crosshead forces in the cure. Metal piles are often used in re- sign process to reduce the likelihood of compressor, said Pak and Howes. Other mote locations because of the difficulty vibration in reciprocating and rotating types of vibration may also arise, such of obtaining concrete. compressors. First, a site and equip- as vibrating cylinders, scrubbers, bottles Primus recommends that if piles are ment ANALYSIS must be completed. and piping. These are often the result of used, a pre-cast concrete slab be in- Second, a dynamic FOUNDATION ANALYSIS poor support or the equipment being stalled on top of the piles.
6 This option should be performed to identify where operated at or near their resonance. provides a more forgiving DESIGN while FOUNDATION stiffness is required to avoid These forces and their location on offering a large contact surface to sup- resonance of machine components. the skid are then incorporated into a port the skid package. Steel plates can And finally, field implementation must dynamic ANALYSIS , which can be per- be embedded onto the top of the con- be carefully managed to ensure foun- formed by Beta or Primus. The result crete and used for welding the skid to dations are properly installed and con- is a recommended DESIGN that resists the slab. As well, plates can be in- nected to the package's skid members. forces and adds stiffness in areas sup- stalled for welding the skid under When Primus performs a founda- porting key machine components.
7 Scrubbers, pipe clamps, bottles and tion ANALYSIS , a series of factors are The required stiffness is critical to building columns to the concrete base. taken into consideration. First, testing avoiding resonances in certain areas, After the piles have been driven to is performed to determine the proper- such as scrubber bases and cylinder their designed depth, they should be ties of the soil at the proposed site. assembly supports. cut to the proper elevation and Next, data on the type of equipment The FOUNDATION DESIGN may entail capped. Pile stick-up above the ground to be used at the site are gathered. All the construction of an engineered should be minimized wherever possi- of this information is required to de- gravel pad. Pads are normally cheap ble, since the amount of stick-up ad- termine the dynamic response of the to install, but do not always provide versely affects the lateral stiffness of FOUNDATION system.
8 Good solid contact between the pack- the piles. When compressor skids are In a package using a reciprocating age skid and the gravel pad that is nec- welded directly onto metal piles, the compressor, for example, the model of compressor, the number of throws, cylinder sizes and the speed of the equipment determines the dynamic forces and couples produced during operation. In the majority of larger com- pressors, opposing pistons are mounted Image courtesy of Beta Machinery ANALYSIS . horizontally and offset ( , the center line of the pistons do not line up). Since opposing pistons are connected to the same crankshaft and travel in and out together, the forces they create al- most cancel each other. But even though the forces are minimal, the pis- tons create torque as they travel out- ward, and create torque in the opposite direction when they travel inward.
9 It is this action by the pistons that creates unbalanced forces and couples in the compressor, and it is these forces that cause the biggest vibration concern when designing foundations . Besides In this field project, the FOUNDATION was modified. A beam was added under the skid and welded mechanical causes, unbalance forces to the existing piles. By adding an extra beam, stiffness was provided midspan to support the can also be induced by pulsating gas in equipment above it. If a FOUNDATION ANALYSIS and DESIGN had been completed before construction , the system, counterweights on the a pile would have been installed at that location. APRIL-MAY 2006 COMPRESSORTechTwo 5/10/06 10:18 AM Page 3. calmed down by merely adjusting or making small repairs to the equipment, or by making a minor modification to the package. If not, the problem may involve more extensive repairs to the FOUNDATION or stiffening of the skid.
10 One solution used to decrease vi- bration in a package is to add a beam Image courtesy of Primus Consulting. along the bottom of a skid using the existing piles. By installing an addi- tional beam, stiffness can be provided midspan to support the equipment above it, which reduces the resonance and resulting vibration. The beam is slid under the package and lifted. It is deformed by jacking up the middle, then welded into place. All repairs oc- cur while working in the crawlspace between the package and the ground. This solution is generally used when Pre-cast concrete slabs can be constructed with steel plates embedded onto the top of the there are not enough piles or the ex- concrete. These plates are used for welding the skid onto the slab. Plates are also installed for isting piles are incorrectly located, welding the skid under scrubbers, pipe clamps, bottles and building columns.